Alright so now that you have a good story to tell people, it's almost time to start applying for jobs.
You are going to need a resume. Although some gyms may not require it, you'll look professional if you have a resume.
Like a lot of things in life, the best approach is to look at how other people did it. So, type "personal training resume" into whatever search engine you prefer, and start taking a look. Spend some time checking out the many examples you'll find posted online and get an idea of the different formatting options, look at what information is being included, etc.
Really take a detailed look at your history since high school and use your imagination to figure out how to include your life experiences on your resume. Even if was not paid work, you can always list it under "proficiencies" or "qualifications".
Once you've gathered all this information, if possible, try to get some help putting your resume together. High schools and colleges often have resources to help you with this. If you have a parent or older sibling or even a friend that you think knows how to put together a good resume, ask for some help from them. Another resource is online help. There are websites that have many varieties of templates that make assembling a good resume very easy.
So take a day or two to assemble your resume. Once that's done, check back here and we'll move on to the next step!